Printing inks are conventionally prepared by a series of steps that comprise (1) reacting the starting ingredients for the pigment in an agitated vessel to obtain a slurry containing about 1 to 3 percent of pigment in mother liquor, (2) filtering and washing the liquid reaction product of step (1) with water to remove the mother liquor and decrease the amount of water-soluble by-products to an acceptable level, forming a presscake that contains about 20 percent of pigment and 80 percent of water, (3) putting the presscake from step (2) into a high horsepower, high shear mixer for at least 15 hours to transfer the pigment from the aqueous phase to a non-aqueous phase to effect complete dispersion of the pigment in the non-aqueous phase, and (4) finally adjusting the batch by adding materials to insure proper rheology and color characteristics to meet the requirements of the printing ink manufacturer.
The pigment flush product from step (4) is then sold to the manufacturer of printing inks who then, at a different location, (5) mixes the pigment with additional varnish, e.g., resin, solvent, and, optionally, a drying oil, and conventional additives to prepare a printing ink that meets the customer's requirements.
Alternately, the pigment presscake from step (2) may be dried, the dry product mixed with the non-aqueous components, and the resulting paste subjected to high shear in dispersion equipment, such as a three-roll mill.